It has been well known that Chlorella algae, which belong to the species of unicellular Chlorophyceae, are used for the purposes of preparing food or food additives in a form of the algae per se or the extracted solution thereof. It has also been known that .beta.-carotene, which is found in large quantities in Dunaliella algae belonging to the same species as Chlorella algae, is utilized in the form of a suspension in vegetable oil as natural coloring agents for food, cosmetics, feed and the like or as a nourishing substance. However, no practical proposal had been made concerning the method of utilizing Dunaliella algae per se for health-oriented food without destroying the .beta.-carotene occurring therein.
Dunaliella algae contain proteins, sugars, lipids, iron, vitamins and a variety of other physiologically active ingredients. As to vitamins, Dunaliella algae produce a lot of .beta.-carotene therein by growing the algae in a culture fluid containing a high concentration of salt and a small amount of nitrogen under intense light from sunbeams and other appropriate conditions. .beta.-carotene is a provitamin A compound having conjugated double bands. Accordingly, .beta.-carotene is oxygen-, heat-, and light-labile. This presents a serious problem in the manufacture of health food containing Dunaliella algae. It has therefore been strongly desired to develop a method by which the algae can be processed without destroying natural .beta.-carotene and the product obtained preserved in a stable state.
The present inventor actively investigated possible solutions for the aforementioned problems. As the result of such investigation, he has completed the present invention.